The motor control device that controls the speed and position of a motor generally performs a speed proportional-integral (PI) control or a control with a feedback loop that is configured using a filter or the like. Control constants that define characteristics of these controls need to be set according to characteristics of a mechanical system to be driven, and thus it is desired that high-speed and high-accuracy control be realized with setting and/or adjustment as simple as possible.
To satisfy this desire, for example, Patent Literature 1 discloses a technique related to a motor control device that has a speed control unit that performs PI control, a torque filter unit in which a low-pass filter is commonly used, and the like, and sets various control constants for setting characteristics of these units based on one parameter inputted from the external according to a specific relational expression.
Meanwhile, when the low-pass filter as in the above is used, stable control is difficult in a case where a mechanical system to be driven has a low rigidity and higher inertia than that of the motor. To solve this problem, a technique intended for a mechanical system which is two-inertia system having a larger load is disclosed in Patent Literature 2.
According to the technique described in Patent Literature 2, a proportional gain (speed gain) of a speed control unit can be stably increased using a phase-lag filter having characteristics that the frequency response gain is constant in a low-frequency region lower than a set first filter frequency and in a high-frequency region higher than a set second filter frequency and that phase lag occurs and the frequency response gain decreases with increase in frequency in an intermediate frequency region therebetween. The “frequency response gain” is hereinafter referred to simply as “gain” when there is no potential for confusion. Patent Literature 2 also discloses a technique in which a parameter set unit is provided to enable to automatically set the first filter frequency and the second filter frequency. As a set method of these frequencies, there is disclosed a method in which the first and second filter frequencies are set based on the proportional gain (speed gain) of the speed control unit, an inertia value of the whole mechanical system and an inertia value of the motor itself with reference to a first crossover frequency ωC1 considered in terms of the inertia of the whole mechanical system and a second crossover frequency ωC2 considered in terms of the inertia of only the motor. Alternatively, there is also disclosed a method in which the frequencies are set with reference to an antiresonant frequency or resonant frequency of the mechanical system.